Automated continuous classification and reblending system for sand and other granular material

ABSTRACT

A continuous-operation automated control system for a water scalping tank or like apparatus in which granular material of different sizes accumulates at varying rates at a series of classification stations; the material is discharged to at least one specification reblending flume, in predetermined ratios, to produce a specification product, and excess material is discharged to an auxiliary flume. One classification station is designated a master station. Discharge at each station is initiated whenever sufficient material has accumulated to allow a relatively constant flow. Each station has a digital timer for measuring its flow to the specification product; the time of flow for the master station is continuously compared with the flow time for each secondary station in a pre-set ratio that may be different for each secondary station. When the comparison for any secondary station shows excessive cumulative flow from that station, its discharge is diverted from the specification flume to the auxiliary flume, but only until the master station flow catches up. When the comparison for any secondary station shows an inadequate cumulative flow, the master station discharge is diverted to the auxiliary flume until the secondary stations have all caught up.

United States Patent [1 1 McCauley Oct. 21, 1975 [57] ABSTRACT A continuous-operation automated control system for a water scalping tank or like apparatus in which gran- [75] Inventor; Porter Thompson McCaul ular material of different sizes accumulates at varying Winnetka, lll. rates at a series of classification stations; the material is discharged to at least one specification reblending [73] Asslgnee: Eagle Iron works Des Momes flume, in predetermined ratios, to produce a specificalowa tion product, and excess material is discharged to an [22] Filed: Dec. 18, 1974 auxiliary flume. One classification station is designated a master station. Dischar e at each station is initiated [2H Appl' 533802 whenever sufficient material has accumulated to allow a relatively constant flow. Each station has a digital [52] US. Cl. 222/64; 222/70; 222/1445 timer for measuring its flow to the specification prod- [51] Int. Cl. B671) 5/08 h time f fl f h m er ion i c n inu- [58] Field of Search 222/70, 132, 1445, 129, ously compared with the flow time for each secondary 222/64; 209/ l 56 station in a pre-set ratio that may be different for each secondary station. When the comparison for any sec- [56] References Cited ondary station shows excessive cumulative flow from UNITED STATES PATENTS that station, its discharge is diverted from the specifi- 3,l 14,479 12/1963 Keeney 222/132 x to the aux'l'ary flume but only ""l 3,129.84) 4/1964 Cochran 222/64 master statlon flow catches up. When the comparison 3,160.32 12/1964 Cochran I. for any secondary station shows an inadequate cumu- 3 7 23 9 9 Archer 222/70 lative flow, the master station discharge is diverted to Primary Examiner-Allen N. Knowles Attorney, Agent, or Firm-Kinzer, Plyer, Dorn &

the auxiliary flume until the secondary stations have all caught up.

10 Claims, 9 Drawing Figures McEachran 3 low l 1| as ma 46C 4 2 I Y j I l 2 US. Patent Oct. 21, 1975 lo T- Sheet 1 of 5 OUTLET US. Patent Oct. 21, 1975 Sheet 4 of5 3,913,788

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B DIvERSION 5 54 PRODUCT B PRODUCT B ACTUATOR T RATIO ERROR 685 302 5448 CONTROL 1 B REGISTER PROD. B 1

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PROD. A PRODUCT B PRODUCT E; DIVERSION S RATIO ERROR ACTUATOR T CONTROL 86 REGISTER 8B 303 64457 A STATION 222 STATION222 T 845 L/ q? PROD. B L 8'8 878 DIvERSION MA 928 ACTUATOR PRODUCT A \PRODUCT A W 304 644C N RATIO |O6A IOQA ERROR 06A 7 2 I CONTROL SBI'EI9I'ISLES3 L OUTLET 2 STATKZN 22s IOEZBA ACTUATORJZ II2B 744A) PRODUCT B PRODUCT B RATIO 4 ERROR SE 3 f CONTROL I REGISTER I085 ACTUATOR S I STATION 23 I S I I IIO IOABV 107B 305 7445 A I J v T IOIB PROD. B

DIvERSION o ACTUATOR N 306 /744C 2 STATION 2 24 STATION STAT|ON22 2 STATION 223 OUTLET 2 3 SENSOR SENSOR SENSOR SENSOR ACTUATOR I2 I 23 I J AUTOMATED CONTINUOUS CLASSIFICATION AND REBLENDING SYSTEM FOR SAND AND OTHER GRANULAR MATERIAL BACKGROUND OF THE INVENTION In a water scalping tank, employed for classification and reblending of sand or other water-insoluble granular material, a slurry of sand and water is introduced into one end of an elongated tank; the larger particles settle to the bottom near the input end and progressively finer particles settle out toward the opposite (overflow) end of the tank. A series of classification stations for discharge of sand are spaced longitudinally of the tank. Sand is permitted to accumulate to a substantial depth and is then discharged from each station to one or more reblending flumes. The tank may be equipped with one flume for blending a specification product and a second flume for disposing of excess sand not used in in the specification product. In many instances, the tank has two specification product flumes and an auxiliary flume for the excess sand.

The water scalping tank serves three basic functions. One is to remove excess water from the sand or other granular material. The second function is to classify the sand into various sizes. The third function is to reblend these different sand sizes in predetermined ratio to meet a quantitative specification. Ideally, the tank would separate the sand into non-overlapping sizes. In actual practice, the sand discharged at each classification station may include several different particle sizes, but there is sufficient differentiation in particle size between the stations to permit reblending within rather closely controlled tolerances.

The most common reblending control for a water scalping tank or similar classifying and reblending apparatus comprises a series of manually adjustable splitter gates, one for each classification station. In many installations, however, variations in the gradation of the material fed to the tank may result in substantial fluctuations in the rate of material accumulation at the various classification stations. This necessitates frequent sampling of the reblended specification product, followed by manual readjustment of the splitter gates to hold the composition of the product within the specification. This sampling and readjustment operation is time consuming and wasteful. Moreover, if the input gradation changes fairly rapidly, it may be literally impossible for the operator to effect a manual adjustment quickly enough to stay within the specification.

One highly successful automated control system for a water scalping sand classifying and reblending tank is described in Cochran U.S. Pat. No. 3,160,32l, issued Dec. 8, 1964. In the Cochran system, the specification product is produced in a series of batches. The quantitative ratio between the amounts of sand discharged from the classification stations to the specification product is determined by individual timers, one for each classification station, all of which must time out before a new batch is started. The Cochran system can produce two or more specification products, on either a simultaneous basis or a sequential basis; each product is prepared as a series of batches of predetermined proportions. The Cochran system also provides an effective tolerance control, utilizing a maximum timer and a minimum timer for each classification station of the tank. The Cochran patent illustrates a tank having plural outlet valves at each classification station, one valve for each reblending flume. A similar batch control, applied to a tank in which each classification station has a single outlet valve and a diversion valve for directing the flow to two or more different flumes, is shown in Archer U.S. Pat. No. 3,467,281.

Automated control of reblending in a water scalping sand classifying tank or similar apparatus, on a continuous basis, has not previously been available. A principal difficulty results from the fact that sand does not accumulate at a constant rate, at the different classification stations of the tank, necessitating intermittent discharge at varying times from the different classification stations. Effective tolerance control, which is highly important in maintaining a quality specification product while minimizing the discharge of excess sand to a waste or auxiliary product, has required the use of two timers for each classification station, thus adding materially to the cost of the automated control equipment. The achievement of effective tolerance control, without requiring duplication of the timing or other measuring apparatus, is highly desirable but has not been readily feasible with previously known systems. In essence, what is needed is a low-cost automated electronic control that operates on a continuous flow basis with effective tolerance control to minimize waste.

SUMMARY OF THE INVENTION It is a principal object of the present invention, therefore, to provide a new and improved fully automated control for a water scalping tank or like apparatus for classifying and reblending granular materials in accordance with a quantitative ratio specification, that operates on a continuous basis and that effectively compensates for any changes in the gradation of material supplied to the apparatus, whether the change occurs on a long term or a short term basis.

A further object of the invention is to provide a new and improved control system for a water scalping tank or like classifying and reblending apparatus that affords the advantages of essentially complete automation, including compensation for changes in input gradation, and that permits effective control of maximum and minimum tolerances for a specification product without requiring duplicate timing or other measuring apparatus for the individual classification stations of the apparatus.

A specific object of the invention is to provide a new and improved electronic digital control system of relatively simple construction that affords an effective and accurate automated control for producing a specification product from a water scalping tank or like apparatus for classifying and reblending granular material.

Accordingly, the invention relates to a control system for a water scalping tank or like apparatus for classifying and reblending granular material in accordance with a quantitative ratio specification, of the kind including a master classification station and a series of secondary classification stations at which different classes of material accumulate at varying rates, each station including a sensor for developing a discharge signal indicative of the presence of sufficient accumulated material to allow discharge at a relatively constant rate for a minimum time interval, each station further including discharge means actuatable between a closed condition in which no material is discharged from the station, a normal discharge condition in which material is discharged to a specification reblending flume or other receptacle, and an auxiliary discharge condition in which material is discharged to an auxiliary receptacle. The control system comprises a plurality of actuating means, one for each classification station, for actuating the discharge means for that station from its closed condition to a discharge condition in response to a discharge signal from the sensor for that station. The actuating means further actuates the discharge means for that station from its normal discharge condition to its auxiliary discharge condition in response to a diversion signal. A plurality of timing means are provided, one for each classification station, for generating a timing signal representative of the time that the classification station is in its normal discharge condition. A series of comparator means are included in the control system, each including a settable ratio control, there being one comparator for each secondary classification station. Each comparator continuously compares the master station timing signal in preset ratio with the timing signal for its secondary station and develops an excess signal whenever there is an excessive discharge from the secondary station to the specification receptacle. The excess signal from each secondary station is applied to the actuating means for that station as a diversion signal. The comparator also develops a deficiency signal whenever there is an inadequate discharge from its secondary station to the specification receptacle. The control system further comprises means, coupled to all of the comparators, for applying a diversion signal to the actuating means of the master station upon occurrence of a deficiency signal from any of the comparators.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional plan view of one form of water scalping tank in which a control system constructed in accordance with the present invention may be incorporated, taken approximately along line l1 in FIG. 2;

FIG. 2 is a partially sectional elevation view of a water scalping tank taken approximately as indicated by line 22 in FIG. 1;

FIG. 3 is a transverse sectional elevational view of the water scalping tank taken approximately as indicated by line 33 in FIG. 1;

FIG. 4 is a transverse sectional view, similar to FIG. 3. illustrating a different discharge valve arrangement that may be utilized at each classification station of the tank;

FIG. 5 is a logic schematic, partly in block diagram form, of a simplified control system constructed in accordance with one embodiment of the present invention, applicable to a tank similar to that of FIGS. 1-3 when employed for the preparation of a single specification product and an auxiliary product;

FIG. 6 is a detailed logic circuit diagram of the control for a master classification station, in the system of FIG. 5, including timing clock for the system;

FIG. 7 is a detailed logic circuit diagram of the ratio and tolerance control components for a secondary classification station in the control system of FIG. 5;

FIG. 8 is a logic diagram, partly in block form, of a control system for the scalping tank of FIGS. 1-3, constructed in accordance with the invention and capable of preparing two specification products on a simultaneous basis; and

FIG. 9 is a logic diagram, partly in block form, of a control system constructed in accordance with the invention and applicable to a tank utilizing the construction modification illustrated in FIG. 4, producing two specification products on a sequential basis.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1, 2 and 3 illustrate, in simplified form, one embodiment of a water scalping sand classifying and reblending tank in which a control system constructed in accordance with the present invention may be incorporated. The scalping tank 10 includes a basic tank structure comprising an input or coarse sand section 11 and an outlet or fine sand section 12. A feed box 13 is mounted on the end of the input section 11 and an input conduit 14 is connected to the feed box. Feed box 13 has an outlet opening 15 communicating with the interior of tank section II. Scalping tank 10 may also be provided with an auxiliary water inlet 16, preferable located in the input section 11 of the tank as shown in FIG. 2.

Tank 10 has six classification stations 21 through 26, displaced from each other along the bottom of the tank from the inlet end of the tank to the outlet end. At the outlet end of the tank, there is an overflow conduit 28 for removing excess water from the tank.

All of the sand classification stations 21-26 are essentially similar in construction. A typical classification station 24, as shown in FIG. 3, includes a sensor 31 for sensing the presence of a sufficient accumulation of sand to allow discharge from the classification station at a relatively constant rate for at least a minimum time interval entailed in opening and closing a discharge valve. Sensor 31 may be of conventional construction, comprising a sensing paddle 32 mounted on the lower end of a shaft 33 that projects vertically through the section of the tank in which station 24 is located. Shaft 33 extends through a guard 35 and is connected to a stall motor 34 that continuously drives the shaft. Motor 34 is electrically or mechanically connected to a sensing switch (not shown) actuated whenever there is a sufficient accumulation of sand or other granular material 36 to prevent continuing rotation of sensing paddle 32 and stall the motor 34. In this manner, sensor 31 develops an electrical signal, referred to herein as a discharge signal, whenever the accumulated material 36 is adequate to allow discharge of sand from classification station 25 at a relatively constant rate; whenever the sand supply 36 is depleted by discharge to a level at which paddle 32 can resume rotation, the discharge signal is terminated.

The typical classification station 24 (FIG. 3) includes means for discharging accumulated sand from the tank. In the construction shown in FIG. 3, this discharge means comprises three individual outlet valves 41A, 41B, and 41C in the bottom of tank 10. Discharge valve 41A comprises a valve closure member 42A connected to an operating rod 43A that extends upward through the tank and is connected to a solenoid-operated hydraulic valve actuator 44A. Similarly, valve 418 comprises a valve closure member 42B connected to an operating rod 438 that is in turn connected to a solenoidoperated hydraulic valve actuator 448. For discharge valve 41C, the principal components are a closure member 42C, an actuator 44C, and an operating rod 43C which connects the closure member to the actuator. Valves 41A-41C are individually connected to three discharge conduits 45A, 45B, and 45C, respectively.

Reblending of sand from tank takes place in three reblending flumes or receptacles46A, 46B, and 46C. As shown in FIGS. 1 and 3, flume 46A is aligned with the discharge valve 41A at station 24 and with a similarly situated discharge valve at each of the other classification stations 21-23, 25, and 26 of tank 10. Similarly, flume 46B is aligned with valve 418 and with its own individual discharge valve at each classification station. Flume 46C, sometimes referred to as the auxiliary flume, is aligned with the central discharge valve at each classification station of the tank. Individual outlets 47A, 47B, and 47C are provided for the reblending flumes 46A, 46B, and 46C respectively (FIGS. 2 and 3).

In operation, a slurry of sand and water is fed into feed box 13 through conduit 14 and flows into tank 10 through opening 15. Simultaneously, additional water may be supplied to the tank through conduit 16. As the slurry flows out of opening 15, the heavier particles settle most rapidly toward the bottom of the tank. Finer particles settle out more slowly. In this manner, sand accumulates on the bottom of the tank, the largest sand particles accumulating at the initial classification stations 21 and 22 and the finest sand settling out at the final classification station 26. The actual number of classification stations in the tank may vary, depending on the length and capacity of the tank; in most commercial installations, the number of classification stations is between six and twelve. With the flow of sand and water properly balanced, as by adjustment of the water input through conduit 16, virtually all of the sand settles to the bottom of the tank and the overflow of water into outlet conduit 28 is essentially free of sand.

When scalping tank 10 is in operation, all of the sensor motors such as motor 34 (FIG. 3) are energized. These motors rotate the sensor paddles relatively freely in the water. With particular reference to classification station 24 (FIG. 3), the sand accumulation 36 eventually reaches a level at which it interferes with rotation of the sensing paddle 32. When this occurs, motor 34 stalls, actuating a sensing switch or other signal device connected to the motor to develop a discharge signal as described above. The discharge signal from sensor 31 is utilized to operate one or more of the actuators 44A-44C, opening at least one of the outlet valves 41A- 41C. The resulting discharge, into one or more of the flumes 46A-46C, reduces the level of sand at station 24 and eventually frees paddle 32 for continuing rotation. As soon as paddle 32 resumes rotation, the discharge signal from sensor 31 is interrupted and actuators 44A- 44C operate to close all of the discharge valves 41A- 41C so that additional sand can accumulate at station 24. This process continues throughout the operation of scalping tank 10. The control system of the present invention, affording selective control of the discharge means comprising valves 41A-41C, provides for the controlled discharge of sand of given constituency into flumes 46A-46C to produce either one or two specification products.

FIG. 5 illustrates a control system 50 affording fully automated control for a water scalping tank or like apparatus for classifying and reblending granular material, such as the water scalping tank 10 of FIGS. 1-3. Control system 50 prepares only a single specification product and discharges all excess material to an auxiliary product. Thus, with system 50, the classifier uses only one specification reblending receptacle, in this instance the reblending flume 46A (FIG. 3). An auxiliary receptacle, flume 46C, is also utilized, but the remaining flume 46B is not employed. In conjunction with control system 50 (FIG. 5) the specification product is sometimes referred to as Product A and the auxiliary or waste product is identified as Product C. Control system 50 includes the actuating means for each of the classification stations of the scalping tank (e.g. actuators 44A and 44C of station 24) and also includes the sensors for all of the classification stations.

In setting up control system 50, one of the classification stations 21-26 of the scalping tank is selected as a master station. In the ensuing description, classification station 24 is taken as the master classification station, and stations 21-23, 25 and 26 are identified as secondary classification stations. This designation of master and secondary stations is quite arbitrary; any one of the classification stations 21-26 could be chosen as the master station and connected accordingly into control system 50.

Control system 50 comprises a clock signal source 51 constituting the time base for the system. Clock source 51 may comprise a conventional oscillator or other circuit capable or producing a train of digital pulses recurring at a constant frequency. High frequency operation is not necessary or even particularly desirable; the operating frequency for clock source 51 may, for example, be as low as ten Hertz. The general nature of the clock signal developed by source 51 is indicated by the waveform 53, and appears at the output of circuit 51.

Control system 50 further comprises a master station timing means comprising an AND gate 54. AND gate 54 has three inputs. One input to gate 54 is connected to the output 52 of the clock source 51. A second input to the master station timing gate 54 is derived from sensor 31 for classification station 24. The third input to ANd gate 54, which is an inhibit input, is described more fully hereinafter.

The output 55 of AND gate 54 is connected to a ratio control circuit 61 that is a part of the control for the secondary classification station 21. Ratio control circuit 61 may comprise any counter or frequency-divider circuit which can be preset to produce an output signal, at its output 62, in a predetermined count ratio with respect to the input signal supplied to the control. Output 62 of circuit 61 is connected to the down" input of an up-down counter 63 that is incorporated in an error register 64 for the secondary classification station 21.

The up'- input of counter 63 is connected to the output 65 of a timing means for the secondary classification station 21, in this instance comprising an AND gate 66. The timing AND gate 66 has three inputs. One is a continuous clock signal input derived from the output 52 of clock source 51. A second input to AND gate 66 is derived from a sensor 131 associated with the secondary classification station 21, which develops a discharge signal for that secondary station. The third in put to AND gate 66 is an inhibit input described more fully hereinafter.

Error register 64 further comprises two decoding AND gates 67 and 68. Gates 67 and 68 are utilized to identify a deficiency or an excess, respectively, in the quantity of granular material discharged to the specifi cation product A from station 21 relative to the quantity of sand discharged to product A from master station 24. AND gates 67 and 68, depending upon their connections to the up-down counter 63, also define tolerance limits for the quantities of material discharged to the specification product from secondary station 21 in relation to the specification product quantities discharged from master station 24. For purposes of explanation, a tolerance of plus or minus four percent has been selected, in conjunction with counter operation predicated on a total count of one hundred. For this arrangement, gate 67 produces a deficiency signal in response to a negative count of four in the up-down counter 63. Similarly, AND gate 68 develops an excess signal whenever there is a positive count of four in counter 63. The excess signal output from AND gate 68 is coupled back to the input of AND gate 66, through an amplifier 69, as an inhibit signal.

The sand discharge actuating means for secondary station 21, in control system 50 (FIG. comprises a product A discharge valve actuator 144A and an auxiliary product C discharge valve actuator 144C. Actuator 144A is connected to the output of an AND circuit 71. AND gate 71 has two inputs; one is connected to the sensor 131 for classification station 21. The second input to AND gate 71 is an inhibit input afforded by an inverting amplifier 72 having its input connected to the output of AND gate 68 in error register 64. Actuator 144C is connected to the output of an AND gate 73. There are two inputs to gate 73, one connected to sensor 131 and the other connected to the output of AND gate 68 in error register 64.

In control system 50, the control for the secondary classification station 22 is essentially similar to that described above for station 21. This portion of the control system comprises a ratio control circuit 81 having an input connected to the output 55 of the master station timing means, AND gate 54. The output 82 of ratio control circuit 81 is connected to the "down" input of an up-down counter 83 incorporated in an error register 84. The up" input to counter 83 is connected to the output 85 of a timing AND gate 86. AND gate 86 has a clock input connected to the output 52 of clock source 51. A second input to the timing AND gate 86 is connected to a sensor 231 for secondary classification station 22. Counter 83 is connected to a first AND gate 87 for developing a deficiency signal and to a second AND gate 88 for developing an excess signal. The output of and gate 88 is coupled to an amplifier 89 that is connected back to the third input of the timing means for station 22, AND gate 86.

The output of AND gate 88 is connected to an inverting amplifier 92 which is in turn connected to one input of an AND gate 91. The second input to AND gate 91 is the discharge signal for station 22 taken from sensor 231. The output of AND gate 91 is connected to a discharge valve actuator 144A which controls the discharge of sand from station 22 to the spcification product flume ofthe scalping tank. The output of AND gate 88 is also connected, without inversion, to one input of an AND gate 93 that has a second input taken from sensor 231. The output of AND gate 93 is connected to a control solenoid or other suitable actuator 244C that controls the discharge of sand from station 22 to the auxiliary or waste flume 46C of the scalping tank.

The control for the secondary classification station 23, in system 50, corresponds to that described above for stations 21 and 22. It includes a ratio control circuit 101 connected to an llp-ClOWl'I counter 103 in an error register 104; register 104 has a deficiency output AND gate 107 and an excess output AND gate 108. As before, the timing means for this portion of the control system comprises an AND gate 106. One input of gate 106 is supplied from an amplifier 109 connected to the output of the excess AND gate 108. Another input to gate 106 is taken from clock source 51, and a third input to gate 106 is connected to a sensor 331 for station 23. The specification product actuator 344A for station 23 is controlled by an AND gate 111. One input for gate 111 is connected to an inverting amplifier 112 connected to the output of AND gate 108. The auxiliary product actuator 344C for station 23 is controlled by an AND gate 113 having a direct input connection from gate 108. Gates 111 and 113 each have an input from sensor 331.

Because the portions of control system 50 associated with the remaining secondary stations 25 and 26 (FIGS. 1 and 2) duplicate those for stations 21-23, the remainder of the control system has not been illustrated in FIG. 5.

The portion of control system 50 that actuates the master classification station 24 includes an OR gate 124 having a plurality of inputs, each connected to the deficiency decoder AND gate for one secondary classification station. Thus, OR gate 124 has an input connection from AND gate 67 in error register 64, another input connection from AND gate 87 in error register 84, a third input from AND gate 107 in error register 104, etc. The output of OR gate 124 is connected to an inverting amplifier which is in turn coupled to one input of the master station timing gate 54 to afford an inhibit signal for that gate.

The output of OR gate 124 is also connected to an inverting amplifier 122 having its output connected to one input of AND gate 121. A second input to AND gate 121 is connected to sensor 31. The output of AND gate 121 is connected to the actuator 44A that controls the discharge of sand from the master classification station 24 to the specification product flume 46A (FIG. 3).

The output of OR gate 124 (FIG. 5) is directly connected to one input of an AND gate 123 that is connected to the actuator 44C which controls the discharge of sand from station 24 to the auxiliary flume or receptacle 46C (FIG. 3). The second input to AND gate 123 is the discharge signal for station 24, taken from sensor 31.

The operation of control system 50 is based upon the fundamental assumption that the quantity of sand or other granular material discharged through any one of the discharge valves of tank 10 is approximately proportional to the length of time that the valve is held open. This assumption is basically sound in practice. For system 50, the discharge of sand through valve 41A (FIG. 3), controlled by actuator 44A, is treated as an independent variable. The quantities of sand discharged to the specification product flume 46A from the other classification stations of the tank, stations 21-23, 25 and 26, are treated as dependent variables. Basically, control system 50 operates to discharge material from station 24 to Product A whenever there is an adequate accumulation of material, as long as the quantities of material discharged from all of the secondary classification stations occur at rates sufficient to maintain these dependent variables as preselected fractions of the independent variable. As noted above, the

designation of station 24 as the master classification station with discharge from that station to the specification product flume 46A taken as the independent variable for the system, is quite arbitrary; any one of the classification stations 21-26 can be selected as the master classification station.

In considering operation of control system 50, it may first be assumed that tank has been in operation long enough to accumulate a substantial supply of sand at all of the classification stations. Under these circumstances, when the accumulation at master station 24 is sufficient to stall sensing paddle 32 (FIG. 3), sensor 31 produces a discharge signal that is supplied to the master station timing means, AND gate 54 (FIG. 5). With no inhibit signal supplied to AND gate 54, the clock signal 53 from source 51 is applied to the ratio control 61 for the secondary classification station 21. The number of pulses of the clock signal supplied to ratio control 61 is a measure of the time that gate 54 is open and is also a measure of the time that the specification product actuator 44A is energized and sand is discharged from master station 24 to the specification product flume 46A (FIG. 3). Thus, the output signal from AND gate 54 constitutes a master station timing signal representative of the time that the master classification station 24 is in its normal discharge condition discharging material to the specification flume.

In ratio control 61, the master station timing signal is divided in accordance with a preset ratio. This basis could be accomplished on a frequency division bases or by other techniques; in the illustrated circuit, the division is conveniently effected by counting pulses. Thus, utilizing a counter with an overall capacity of one hundred, and with a preset output ratio, ratio control 61 is set to produce a given number of pulses at its output 62 for each one hundred pulses in the master timing signal. For example, ratio control 61 may be preset to forty, and will produce forty output pulses for each one hundred input pulses, or forty percent of the input count. This count represents forty percent of the time of discharge of material from master classification station 24 to the specification product, Product A, and is applied to the "down" input of the up-down counter 63 in the error register 64 for the secondary classification station 21.

If there is sufficient sand at the secondary classification station 21 to provide for discharge at a relatively constant rate for at least a minimum time, sensor 13] produces a discharge signal that is supplied to AND gates 66 and 71. At this stage of the operation, the dis charge signal from sensor 131 is applied to the Product A actuator 144A for station 21, through AND gate 71, and initiates discharge of sand from station 21 to the specification product flume. The discharge signal is also supplied to the timing means for the secondary classification station 21, comprising AND gate 66. The discharge signal enables AND gate 66, so that the clock signal from source 51 is supplied to the "up" input of counter 63 as long as the discharge signal is available and a discharge of sand from station 21 to the specification product, Product A, continues. The number of pulses in the output signal from AND gate 66 is a direct measure of the time that the secondary classification station 21 is in its normal discharge condition and is supplying sand to the specification product flume 46A.

In counter 63, the pulses in the timing signal for secondary classification station 21 are accumulated as an up count. At the same time, the preset fraction of the pulses from the master station timing signal that are supplied to counter 63 from ratio control 61 are accumulated as a down count. Counter 63 and ratio control 61 together thus comprise a comparator for continuously comparing the master station timing signal in preset ratio with the timing signal for the secondary classification station 21. The comparison is effected by a subtraction operation, such that the count stored in counter 63 at any given time is a measure of the difference in the time the specification product discharge valve for station 21 has actually been open and the time that discharge valve should have been open to discharge the desired preset fraction of the master station discharge into the specification flume. In a typical counter, the error count may be bi-polar in nature so that a negative remainder appears as a tens complement while a positive number appears in conventional form.

AND gates 67 and 68 are an integral part of the comparator means for the secondary classification station 21. These two gates are employed to decode the count in counter 63, on a continuous basis, and are also employed to establish a tolerance for the discharge from station 21 to the specification product, in relation to a quantitative ratio specification. For purposes of explanation, it is assumed that the tolerance is to be plus or minus four percent. For this tolerance, gate 68 decodes a positive count of four in up-down counter 63 as a positive number and produces an excess signal at its output whenever a positive count of four is reached. Gate 67, on the other hand, decodes a negative count in counter 63 and produces an output signal when a negative count of four is present, a count which may appear as the tens complement, six.

If the down count in counter 63 occurs at a rate faster than the up count, indicating that forty percent of the discharge rate for master station 24 is greater than the actual discharge rate for secondary station 21, error register 64 will ultimately accumulate a negative count of four. When this occurs, the output of AND gate 67 becomes a logical one or true" signal, constituting a deficiency signal indicating an inadequate discharge from the secondary classification station 21. This signal is supplied to OR gate 124, producing an output signal from the OR gate that is utilized as a diversion signal for master station 24. This diversion signal from OR gate 124 is inverted in amplifier 122 and is applied to AND gate 121 as an inhibit signal to preclude further discharge of material from the master station to the specification product flume by de-energizing valve actuator 44A. The diversion signal is also supplied to AND gate 123 as an enabling signal, energizing the auxiliary product actuator 44C to open valve 41C and discharge material from master station 24 to auxiliary flume 46C (FIG. 3). Of course, actual discharge from station 24 is also dependent upon the accumulation of sufficient material at the master classification station to support the desired rate of discharge, as signalled by the discharge signal from sensor 131 that is also applied to AND gate 123.

The diversion signal from OR gate 124 is also applied to inverting amplifier 125 and is supplied to the master station timing gate 54 as an inhibiting signal. Consequently, gate 54 is disabled and no longer supplies an output signal to ratio control 61 so that there is no further down" count signal applied to counter 63.

The net result of this action is that material accumulated at the master classification station 24 is discharged to the auxiliary flume of the classification tank while material from secondary station 21 continues to discharge, whenever available, to the specification product flume. However, as the discharge to the speci fication product continues at station 21, timing means 66 continues to apply a timing signal to the "up input of counter 63. As soon as the count in counter 63 ex ceeds the count of minus four required to enable gate 67 (that is, when a count of minus three is reached), the deficit signal output from AND gate 67 is interrupted. When this occurs, the diversion signal output from OR gate 124 is no longer sustained, cutting off the inhibit signal to AND gate 123. Thereafter, further material accumulated at master station 24 is again discharged to the specification product, Product A, and the down count signal to counter 63 in error register 64 is resumed.

The down count supplied to counter 63 from ratio control 61 may occur often enough, over a given period of time, to accumulate a positive count in the counter. This is the condition that occurs whenever the material accumulation at discharge station 21 exceeds the selected criterion of forty percent of the discharge taking place at master station 24. In these circumstances, error register 64 will ultimately accumulate a positive count of four. The output of AND gate 68 then goes positive or true," producing an excess signal indicating that further discharge from station 21 to the specification flume will create an excess of the material from that station in the specification product.

The excess signal from gate 68 is utilized as a diversion signal to control the actuating means for station 21, comprising actuators 144A and 144C. Thus, the excess signal from gate 68 is inverted in circuit 72 and applied to AND gate 71 as an inhibit signal, preventing energization of actuator 144A and hence preventing any further discharge from station 21 to the specification product flume 46A (FIG. 3). The excess signal is also supplied, as an enabling signal, to AND gate 73 (FIG. Consequently, any further discharge from station 21, occurring while the excess signal from AND gate 68 continues, is effected by actuator 144C; the discharge is directed to the waste product flume or recep tacle 46C (FIG. 3).

The excess signal from AND gate 68 is also supplied to inverter 69, which supplies an inhibiting signal to the timing AND gate 66. Accordingly, although further material can be discharged from station 21 (to the waste receptacle 46C as described above), the time of discharge is no longer counted in counter 63. That is, no up" count signal is applied to counter 63.

The result of these operations is that material accumulated at the master classification station 24 is discharged to the specification product flume 46A of the classification tank, whereas material accumulating at the secondary discharge station 21 is discharged to the auxiliary receptacle, flume 46C. The continuing discharge from station 24 to the specification product, however, results in the application of a continuing "down" signal to counter 63 from ratio control 61. When the total count in counter 63 is reduced below the level of plus four that was required to actuate gate 68, the excess signal output from AND gate 68 is interrupted. This indicates that the system is back within tolerance. Since the inhibit signal from inverter 72 is now interrupted, actuator 144A can again operate to provide a specification product discharge from secondary station 21. Gate 73, on the other hand, now has no enabling input from gate 68, and hence cannot actuate circuit 144C, precluding discharge to the auxiliary flume.

Operation of the secondary classification station 22 is the same as described above for station 21. The ratio control 81 is adjusted to any given ratio, from zero up to one hundred percent. Counter 83 in error register 84 receives a down-count signal from ratio control 81 and receives an up-count signal from the timing AND gate 86. The output signal from gate 86 is available only when station 22 is discharging to the specification product, in its normal discharge condition, due to the inhibit circuit connection through inverter 89. If the discharge from station 22 exceeds the desired ratio with respect to that from master station 24, by more than four percent, AND gate 88 produces an excess signal that is supplied to the actuators 244A, 244C to divert subsequent discharge from the specification flume 46A to the auxiliary flume 46C. Conversely, if the discharge to the specification product from station 22 falls more than four percent below requirements, a deficiency signal developed by AND gate 87 is supplied to OR gate 124 and serves as a diversion signal for the actuating means in the master classification station 24, diverting station 24 output to the auxiliary receptacle 46C until such time as station 22 can catch up.

The same kind of operation occurs at each of the remaining stations of system for each station, the excess signal from the station error register constitutes the necessary diversion signal to prevent excessive discharge of material from that station into the specification product. On the other hand, the presence of a deficiency signal at any of the secondary classification stations operates to produce a diversion signal in the output of OR gate 124, diverting the discharge from station 24 to the auxiliary receptacle until the specification product is brought back into balance.

In system 50, FIG. 5, the ratio of the specification product discharge from each secondary classification station to the discharge from master station 24 is established by the ratio control (61, 81, 101, etc.) for the secondary station. The tolerances for excessive or deficient discharge, however, are determined for each secondary station by the error register for that station. Specifically, with the construction shown, the tolerance limits are established by AND gates 67 (deficiency) and 68 (excess) for station 21 and by the similar decoding AND gates for the other classification station. The four percent tolerances referred to above are exemplary only; a wide variety of tolerances can be accommodated.

The tolerance determined by each of the counterdecoding AND gates 67 and 68 is meaningful only in the context of some specified time interval. Thus, over an extended period of time (e.g., a full day of plant operation) the count in counter 63 is virtually certain to exceed the tolerance limits of plus four or minus four, even though the accumulation of material for discharge at station 21 is approximately equal to the ratio established by control unit 61. Stated differently, over a long period of time, the accumulation of material at the two discharge stations 21 and 24 is virtually certain to drift from the ratio set in control 61 to an extent S1111 ficient to produce either an excess or a deficiency signa] from error register 64. The same situation applies for all of the other secondary classification stations.

To avoid such long-term accumulations in the counters 63, 83, etc., and to preserve a true tolerance operation, system 50 may incorporate a provision for periodic resetting of the error registers. In FIG. 5, this is accomplished by a reset control 129, having an input con nected to clock source 51. Control 129 may constitute a counter of relatively large capacity. The output of control 129 is connected to a reset input for each of the counters 63, 83, 103, etc., in the individual error registers for the secondary classification stations of the tank.

Control 129 resets each of the counters after some reasonable period of time, so that deficiencies or excesses of a minor nature cannot accumulate to cause erroneous determinations of excessive or deficient discharge from any of the stations. By way of example, reset control 129 may operate to reset each of the error register counters after a time interval of thirty minutes.

A periodic reset arrangement, such as the control 129, is not the only technique available to preserve a true tolerance control over extended periods of time. Thus, counter 63 may be provided with a reset circuit to reset the counter to zero on the occurrence of a down-count following generation of an excess signal from gate 68. A similar reset circuit is utilized to reset counter 63 to zero on the occurrence of an up-count following generation of a deficiency signal from gate 67. Reset circuits of this type, applied to all of the error registers 64, 84, etc., preclude accumulation of longterm errors in system 50 and assure maximum discharge to the specification product while still maintaining the prescribed tolerance limits.

FIG. 6 illustrates specific circuits that may be utilized for clock 51 and for other controls incorporated in system 50. The illustrated circuits use 54/74 series components, illustrated in terms of NAND/NOR logic.

In the circuit arrangement shown in FIG. 6, clock source 51 comprises two NAND gates 151 and 152. The two imputs for gate 151 are connected together and are connected to a resistor 153 that is returned to ground. Similarly, the two inputs of gates 152 are connected together and are connected to a resistor 154 that is returned to ground. The output of gate 151 is connected to a capacitor 155 that is coupled to the inputs of gate 152. A capacitor 156 couples the output of gate 152 back to the inputs of gate 151. The output 52 for clock source 51 is taken from the output of gate 152, through a NAND gate 157.

As previously noted, the sand accumulation sensors 31, 131, 231, etc., for the different classification stations are usually mechanical switching devices. In virtually any mechanical switch, there is at least a certain minimal amount of bounce." For this reason, a switch bounce suppressor circuit 158 is preferably connected between sensor 31 and timing gate 54, as shown in FIG. 6. The bounce suppressor circuit 158 comprises three NOR gates 159, 161, and 162. One input to gate 159 is taken from the sensing switch 31 (FIG. 3 and 5), the other input to gate 159 being taken from the output of NOR circuit 162. The output of NOR gate 159 is connected through the parallel combination of a resistor 163 and a diode 164, to both of the inputs of NOR gate 161 and to one of the inputs of NOR gate 162. The two inputs of gate 161 are connected to a capacitor 165 that is returned to ground. The output ofNOR gate 161 is connected to the remaining inputs of gate 162 through the parallel combination ofa resistor 166 and a diode 167. This input to gate 162 is also connected to a capacitor 168 that is returned to ground. The output from suppressor circuit 158 is derived from the output of NOR gate 162.

The two cross-connected NAND gates 151 and 152, with resistors 153 and 154 and capacitors 155 and 156, afford a conventional pulse signal source of constant frequency. The bounce suppressor circuit 158 is also conventional; it provides a very limited time delay for the discharge signal from sensor 31 and effectively precludes erroneous actuation of gate 54 which might occur as the result of transient signals developed on actuation of the sensor or caused by other extraneous operations.

In the specific circuit illustrated in FIG. 7, the ratio control circuit 61 for station 21 (see FIG. 5) comprises two binary-coded decimal counters 171 and 172. Counter 171 is connected to a binary-coded decimal units setting switch 173 and counter 172 is connected to a similar BCD tens" switch 174. The two counter circuits 171 and 172 are interconnected in conventional manner to afford a circuit 61 that can be set for any count from zero to ninety-nine; when the count pre-set on the switches 173, 174 is reached, ratio control 61 produces an enabling signal on its output circuit 175.

The output 175 of ratio control 61 is connected to one input ofa NAND gate 176. The other input to gate 176 is derived from the Q output of a flip-flop 177. Flip-flop 177 has a set input connected to the output 55 of the master station timing gate 54 and a reset input connected to the clock circuit 52. A capacitor 178 and resistor 179 are connected to flip-flop 177 to afford a one-shot circuit, the circuit being employed for pulse width control.

The 0 output of flip-flop 177 affords a master timing signal that is applied to one input of a timing NAND gate 66'. A second input to gate 66 is taken from clock circuit 52. A third input is derived from the sand level sensor 131 for station 21 (see FIG. 5), through a bounce suppressor circuit 181 that may be of the same construction as circuit 158 (FIG. 6). A fourth input to timing gate 66' is taken from the excess count gate 68.

The output of timing gate 66 is connected to one input ofa NAND gate 182 incorporated in an error register 64'. A second input to gate 182 is taken from the output of gate 176. Gate 182 has its output connected to both inputs of a NAND gate 183, employed as an inverter. The output of gate 183 is connected to the clock" input of an up-down counter 63' that counts up or down on each clock pulse, depending on the polarity of a signal applied to an up-down" input to the counter. The up-down input for counter 63' is connected to the clock circuit 52.

The l, 2 and 4 outputs of counter 63' are connected to the inputs of the excess" NAND gate 68, in the circuit of FIG. 7. The 1, 2 and 4 outputs of counter 63' are connected to the inputs of the deficiency" NAND gate 67. The output connections for gates 67 and 68 are as shown in FIG. 5.

In order to afford a more explicit example of the operating circuits that may be employed in the invention, specific devices and parameters for the circuits of FIGS. 5 and 6 are set forth below. It should be understood that this information is supplied solely by way of illustration and in no sense as a limitation on the invention.

4'! microfarads 0,1 microfarads FIG. 8 illustrates a control system 150, constructed in accordance with another embodiment of the invention, again affording fully automated control for the water scalping tank 10 of FIGS. 1-3. With system 150, classifier tank 10 (FIGS. 1-3) uses both specification reblending fiumes 46A and 468, as well as the auxiliary flume 46C; the outputs are two specification products and a waste product. in connection with control system 150 (FIG. 8) the specification products are sometimes referred to as Product A and Product B; the auxiliary or waste product is identified as Product C.

In control system 150, classification station 24 is designated as a master station and stations 21-23, 25 and 26 are secondary stations. As before, this designation of master and secondary stations is quite arbitrary; any one of the classification stations 21-26 could be selected as the master station.

Control system 150 comprises a clock signal source 51 which develops a clock signal 53. As before, a relatively low frequency may be utilized for clock source 51. Control system 150 further includes two master sta tion timing means, comprising two AND gates 54A and 5413. One input to each of gates 54A and 54B is connected to the output 52 of clock source 51. A second input to each of the master station timing gates 54A and 54B is derived from the sensor 31 for classification station 24. The third input to each of the gates 54A and 54B is an inhibit input, as described hereinafter.

The output 55A of AND gate 54A is connected to a ratio control circuit 61A that is a part of the control for the secondary classification station 21. Ratio control circuit 61A comprises a counter or frequency-divider circuit which is preset to produce an output signal having a predetermined count ratio with respect to the clock signal 53. Circuit 61A is connected to the down" input of an up-down counter in a Product A error register 64A. The output 55B of timing gate 548 is connected to a ratio control circuit 618. Circuit 6113 is in turn connected to the down' input of an up-down counter in an error register 64B for Product B in station 21.

The up input of error register 64A is connected to the output of a Product A timing means for station 21. an AND gate 66A. Gate 66A has three inputs; one is a continuous clock signal input from clock source 51, a second is derived from the sensor 131 for station 21,

and the third is an inhibit input described more fully hereinafter. The input connections for a Product B timing gate 668 are similar; a clock input, a discharge signal input from sensor 131, and an inhibit input. Gate 668 is the source of up count input signals to error register 64B.

Error register 64A has a deficiency output 67A and an excess" output 68A. Similarly, the Product B error register 648 has a "deficiency output 678 and an excess" output 68B. The two error registers define tolerance limits for the quantities of material discharged to the two specification products from secondary station 21 in relation to the specification product quantities discharged from master station 24. The ratios set in controls 61A and 618 can be the same but are likely to be quite different; the tolerances afforded by registers 64A and 68 can also be different. For purposes of explanation, a tolerance of plus or minus four percent has again been selected for registers 64A and 6413, in conjunction with counter operation predicated on a total count of one hundred. Thus, output 67A produces a deficiency signal in response to a negative count of four in the up-down counter in register 64A, whereas output 68A develops an excess signal whenever there is a positive count of four in register 64A: register 648 works the same way. The excess signal outputs 68A and 68B are coupled back to the inputs of AND gates 66A and 668, respectively, through two inverters 69A and 698, as inhibit signals.

In system 150, the Product A actuator 144A in station 21 is connected to the output of an AND circuit 71A. One input to gate 71A is connected to the sensor 131 for classification station 21; the second input to AND gate 71A is an inhibit input afforded by an inverting amplifier 72A having its input connected to the excess output 68A of error register 64. The Product B actuator 1445 is driven by an AND gate 718 having one input derived from sensor 131 and a second input taken from the excess output 688 of error register 648 through an inverting amplifier 725. The Product C actuator 144C is connected to the output of an AND gate 73. There are three inputs to gate 73; one is connected to sensor 131 and the others are connected to the excess outputs 68A and 68B of error registers 64A and 64B.

In control system 150, the control for the secondary classification station 22 is essentially similar to that for station 21. It comprises two ratio control circuits 81A and 818, for Product A and Product B respectively, having inputs connected to the outputs 55A and 55B, respectively, of the two master station timing gates 54A and 54B. The output of ratio control circuit 81 A is connected to the down input of an up-down counter in an error register 84A. The up input to register 84A is derived from the output of a timing AND gate 86A. AND gate 86A has a clock input taken from the output 52 of clock source 51. A second input to gate 86A is derived from the sensor 231 for station 22. Error register 84A has a deficiency signal output 87A and an excess signal output 88A, the latter being coupled to an inverter 89A that is connected back to the third input of the timing gate 86A. The Product B components for station 22 include the ratio control 818, error register 84B, timing gate 86B, and inverter 898, connected in the same manner as the Product A equipment.

The excess output 88A of register 84A is connected to an inverting amplifier 92A which is in turn connected to one input of an AND gate 91A. The second input to AND gate 91A is the discharge signal for station 22, taken from sensor 231. The output of AND gate 91A is connected to the actuator 244A which controls the discharge of sand from station 22 to the first (Product A) specification flume of the scalping tank, flume 46A (FIG. 3). For Product B, the excess output 88B of error register 84B is connected to an AND gate 91B through an inverter 928. Gate 918, which has its second input connected to sensor 231, controls the Product B valve actuator 2448 that feeds flume 463 from station 22. The excess signals from terminals 88A and 88B are also applied to two inputs of an AND gate 93 that has a third input taken from sensor 231. The output of AND gate 93 is connected to the actuator 244C that controls the discharge of sand from station 22 to the auxiliary flume 46C of the scalping tank.

The control for the secondary classification station 23, in system 150 (FIG. 8), corresponds to those described above for stations 21 and 22. It includes two ratio control circuits 101A and 10113,. for Product A and Product B, connected to two error registers 104A and 10413. Register 104A has a deficiency output 107A and an excess output 108A; register 104B has similar outputs 1078 and 1088. As before, the timing means for this portion of the control system comprises two AND gates 106A and 1068. One input of gate 106A is supplied from an inverter 109A connected to the excess output 108A, another is taken from clock source 51, and the third is connected to the sensor 331 for station 23. Similarly, timing gate 1068 has inputs from clock source 51, from sensor 331, and from excess output 1088 (through an inverter 1098). The specification product actuator 344A for station 23 is controlled by an AND gate 111A: one input for gate 111A is connected to an inverting amplifier 112A connected to the excess output 108A. Another AND gate 111B controls the Product B actuator 3448; its controlling input is derived from excess output 1088, through an inverter 1128. The auxiliary product actuator 344C for station 23 is controlled by an AND gate 113 having direct inputs from terminals 108A and 1088. Gates 111A, 1118, and 113 each have an input from sensor 331.

Because the portions of control system 150 associated with the secondary stations 25 and 26 (FIGS. 1 and 2) duplicate those for stations 21-23, the remainder of the control system has not been illustrated in FIG. 8.

The portion of control system 150 that actuates the master classification station 24 for Product A includes an OR gate 124A having a plurality of inputs, each connected to the deficiency output of the Product A error register for one secondary classification station. Thus, OR gate 124A has input connections from output 67A of error register 64A, from output 87A of error register 84A, from output 107A of error register 104A, etc. For Product B, an OR gate 1248 is provided with an input connection from each of the deficiency outputs 67B, 87B and 1078 of error registers 64B, 84B and 1048, respectively. The output of OR gate 124A is connected, through an inverting amplifier 125A, to one input of the master station Product A timing gate 54A to afford an inhibit signal for that gate. The output of gate 124B is similarly coupled, through an inverter 12513, to one input of gate 548.

The output of OR gate 124A is also connected to an inverting amplifier 122A having its output connected to one input of AND gate 121A. A second input to AND gate 121A is taken from sensor 31. The output of AND gate 121A is connected to the actuator 44A that controls the discharge of sand from the master classification station 24 to the Product A specification flume 46A (see FIG. 3). Gate 1248 is similarly coupled, through an inverter 1228, to an AND gate 1218 that controls the Product B actuator 448 for the master station.

The outputs of OR gates 124A and 1248 are directly connected to two inputs of an AND gate 123 (FIG. 8) that is connected to the actuator 44C which controls the discharge of sand from station 24 to the auxiliary flume or receptacle 46C (FIG. 3). A third input to AND gate 123 is the discharge signal for station 24, taken from sensor 31.

The operation of control system is based upon the same fundamental assumption as system 50, that the quantity of sand or other granular material discharged through any one of the discharge valves of tank 10 is approximately proportional to the length of time that the valve is held open. The quantities of sand discharged through valves 41A and 418 (FIG. 3), controlled by actuators 44A and 448 respectively, are treated as independent variables. The quantities of sand discharged to the specification product flumes 46A and 468 from stations 21-23, 25 and 26 are treated as dependent variables.

In normal operation of classification tank 10, utilizing control system 150, master station 24 discharges sand to both Product A and Product B whenever there is a sufficient accumulation of sand at the master station to provide for an output at a reasonably constant rate. The same operation takes place at each of the secondary classification stations 21-23, 25 and 26. That is, the normal condition for the system entails a discharge to each of the specification product flumes 46A and 463, at each station, whenever an adequate supply of sand is available at the station.

At any given time, if the error register for either product at any secondary station produces an excess signal, indicating that the discharge from that station to that product has become excessive, control system 150 operates to interrupt further discharge from that station to that product until a balanced condition is restored. For example, if more sand has been available at station 22 than is required for Product B, error register 84B produces an excess signal at terminal 88B; the excess signal is applied to gate 913 through inverter 928 to inhibit gate 918. As a consequence, actuator 2448 is de-energized and there is no further discharge to flume 468 from station 22 until the excess signal from register 84B is no longer present. The same action occurs for any excess signal at any station throughout the system.

Whenever any of the error registers for the secondary classification stations produces a deficiency signal, discharge from the master station 24 to the product with which that error register is associated is cut off. Thus, a deficiency signal from any of the Product A error registers 64A, 84A, 104A, etc., produces an output from OR gate 124A that is inverted and applied to AND gate 121A to inhibit gate 121A and prevent energization of actuator 44A. Similarly, a deficiency signal from any of the Product B error registers is used to inhibit gate 121B and prevent energization of actuator 44B.

At any given station in system 150, discharge to the auxiliary flume 46C occurs only when both of the actuators for the specification product flumes 46A and 46B have been cut off. Thus, for master station 24, AND gate 123 can be energized only when a deficiency signal from at least one product A error register occurs in coincidence with a deficiency signal from at least one Product B error register and a discharge signal from sensor 31. This applies also to the secondary classification stations. For example, in station 21, AND gate 73 is enabled only when there is an excess signal from error register 64A, an excess signal from register 64B, and a discharge signal from sensor 131. With this arrangement, Product A and Product B can be prepared in substantial quantities on a simultaneous basis with minimal discharge of sand to auxiliary flume 46C.

To change the constituency of either Product A or Product B, the ratio controls for that product are adjusted, varying the proportions of sand from the different secondary classification stations relative to the quantity of sand from the master classification station. Where loose tolerances are permissible, with respect to one of the specification products, the error registers for that product may be adjusted to permit greater latitude by allowing a higher count before an excess signal or a deficiency signal is generated. Depending upon the specifications that must be met, the tolerance limits may be as low as zero in one direction and may be virtually any desired percentage in the other direction. As in system 50, control system 150 should be equipped with an appropriate reset system to reset all of the error registers in a manner that will preclude long-term error accumulation. The reset arrangement may be the same as described for system 50 and has not been illustrated in FIG. 8.

FIG. 4 illustrates a single classification station 224 for a water scalping sand classifying and reblending tank 210 that is generally similar to tank but utilizes a different mechanical valve arrangement for discharge to the specification product flumes 46A and 46B and the auxiliary (waste) flume 46C. Thus, station 224, which is typical of all stations for tank 210, includes a sand accumulation sensor comprising a sensing paddle 32 mounted on a shaft 33 driven by a stall motor 34. As in tank 10, the flumes 46A-46C are provided with outlets 47A-47C.

Station 224 of tank 210 includes an outlet valve 41 including a casing 43 and an internal valve closure member 42. The valve closure member 42 is actuated between open and closed conditions by compressed air introduced into the interior of casing 43. Valve 41 is connected to a solenoid-operated outlet actuator valve 444C, which is in turn connected to a compressor or other compressed air supply 211. The outlet side of valve 41 is connected to a flexible hose 45 that can be positioned over any of the three flumes 46A-46C.

Station 224 of tank 210 (FIG. 4) further comprises an air-actuated positioning device 212 connected to hose 45 by suitable means such as a ring deflector member 213. Positioning device 212 is connected to a first product diversion actuator valve 444A and to a similar second product diversion actuator valve 444B; valves 444A and 4448 are both connected to air supply 211. When valve 444A is opened, device 212 drives hose 45 to a position over flume 46A to discharge sand to a first specification product, referred to herein as Product A. Opening of valve 4448 causes device 212 to position hose 45 over flume 46B, supplying sand to a second specification product, Product B. With neither actuator valve open, hose 45 is positioned, as shown, over the auxiliary flume 46C.

Except for the outlet valve construction and the apparatus employed to divert the discharge to the different flumes 46A-46C, at each classification station, tank 210 is essentially similar to tank 10. Accordingly, operation of tank 210 need not be described in detail. Tank 210 includes a series of classification stations, usually six to twelve stations depending upon the length of the tank. These stations are numbered 221, 222, 223, 224, et seq., to correspond to stations 21, 22, 23, 24, et. seq. in tank 10 (compare FIG. 8, showing a control for tank 10, with FIG. 9, a control system for tank 210). A tank affording an outlet construction like that of tank 210 is described in Archer US. Pat. No. 3,467,281.

FIG. 9 illustrates a control system 250, constructed in accordance with another embodiment of the invention, that affords fully automated control for the water scalping tank 210 of FIG. 4. With system 250, classifier tank 210 uses both specification reblending flumes 46A and 468, as well as the auxiliary flume 46C; the outputs are two specification products and a waste product. The specification products are sometimes referred to as Product A and Product B; the auxiliary product is identified as Product C.

In control system 250, classification station 224 is designated as a master station and all other classification stations of tank 210 are secondary stations. In FIG. 9, the controls for only four stations 221-224 are illustrated; it should be understood that tank 210 would include additional secondary stations having controls corresponding to those shown for stations 221-223. As before, this designation of master and secondary stations is quite arbitrary; any one of the classification stations of the tank could be selected as the master station.

Control system 250 comprises a clock signal source 51, again operating at a relatively low frequency. Control system 250 includes two master station timing means, comprising two AND gates 54A and 54B. One input to each of gates 54A and 54B is connected to the output 52 of clock source 51. A second input to each of the master station timing gates 54A and 54B is derived from the sensor 31 for classification station 224. The third input to each of the gates 54A and 54B is an inhibit input. Gate 548 has an additional inhibit input, as described hereinafter.

The output 55A of AND gate 54A is connected to a ratio control circuit 61A that is a part of the control for a secondary classification station 221. Ratio control circuit 61A comprises a counter or frequency-divider circuit preset to produce an output signal having a pre determined count ratio with respect to the clock signal. Circuit 61A is connected to the down" input of an updown counter in a Product A error register 64A. The output 558 of timing gate 54B is connected to a Product B ratio control circuit 61B. Circuit 61B is in turn connected to the down input of an up-down counter in an error register 64B for Product 8 in station 221.

The up" input of error register 64A is connected to the output ofa Product A timing means for station 221, an AND gate 66A. Gate 66A has three inputs, a continuous clock signal from source 51, a discharge signal from a sensor 131 for station 221, and an inhibit input described more fully hereinafter. The input connections for a Product B timing gate 668 are similar but specifically different; a clock input taken from source 51 through an AND gate 70, a discharge signal input from sensor 131, and an inhibit input. Gate 70 has a second input described below. Gate 668 is the source of up" count input signals to error register 64B.

The Product A error register 64A has a deficiency" output 67A and an excess" outout 68A. Similarly, the Product B error register 648 has a deficiency outout 67B and an excess output 68B. The two error registers define tolerance limits for the quantities of material discharged to the two specification products from secondary station 221 in relation to the specification product quantities discharged from the master station 224. The ratios set in controls 61A and 61B can be the same or may be quite different; the tolerances afforded by registers 64A and 64B can also be different. For purposes of explanation, a tolerance of plus or minus four percent has again been selected for registers 64A and 643, in conjunction with counter operation predicated on a total count of one hundred. Thus, output 67A produces a deficiency signal in response to a negative count of four in the up-down counter in register 64A, whereas outout 68A develops an excess signal whenever there is a positive count of four in register 64A; register 64B works the same way. The excess signal outputs 68A and 68B are coupled back to the inputs of AND gates 66A and 668, respectively, through two inverters 69A and 69B, as inhibit signals. Moreover, and additional inverter 60 connects the output of inverter 69A to the inhibit input of gate 70.

In system 250, a Product A diversion actuator 544A for station 221, corresponding to actuator 444A in station 24 (FIG. 4), is connected to the excess output 68A of error register 64A through an inverter 72A. the Product B diversion actuator 5448 is driven by an AND gate 302 having one input connected to inverter 72A by an inverter 301. A second input to gate 302 is connected to the excess output 688 of error register 648 through an inverter 72B. The output actuator 544CC is connected to the output of the station 221 sensor 131.

The control for the secondary classification station 222 is essentially similar to that for station 221. It comprises two ratio control circuits 81A and 81B, for Product A and Product B respectively, having inputs connected to the outputs 55A and 558, respectively, of the two master station timing gates 54A and 548. The output of ratio control circuit 81A is connected to the down" input of an up-down counter in an error register 84A. The "up input to register 84A is derived from the output of a timing AND gate 86A. AND gate 86A has a first input taken from clock source 51 and a second input derived from the sensor 231 for station 222. Error register 84A has a deficiency signal output 87A and an excess signal output 88A, the latter being coupled to an inverter 89A that is connected back to the third input of timing gate 86A. The Product B components for station 222 include the ratio control 81B, error register 84B, timing gate 868, and inverter 893, connected in the same manner as the Product A control, except that the clock input to gate 86B is taken through an AND gate 90. An inhibit input to gate 90 is derived from an inverter 80 connected to the output of inverter 89A.

The excess output 88A of register 84A is connected to an inverter 92A, in turn connected to a diversion actuator 644A which controls the discharge of sand from station 222 to the first specification flume of the scalp ing tank, flume 46A (FIG. 4). For Product B, the excess output 88B of error register 84B is connected through an inverter 92B to an AND gate 304; gate 304 has a second input derived from an inverter 303 connected to the output of inverter 92A. Gate 304 is connected to the diversion actuator 6448 that controls the discharge of sand from station 222 to the second specification flume 46B of the scalping tank 210. The outlet actuator 644C for station 222 is connected to the sand level sensor 231 for that station.

The control for the secondary classification station 223, in system 250 (FIG. 9), corresponds to those described above for stations 221 and 222. It includes two ratio control circuits 101A and 1018, for Product A and Product B, connected to two error registers 104A and 104B. Register 104A has a deficiency output 107A and an excess output 108A; register 104B has similar outputs 1078 and 108B. As before, the timing means for this portion of the control system comprises two AND gates 106A and 1068. One input of gate 106A is supplied from an inverter 109A connected to the excess output 108A, another is taken from clock source 51, and the third is connected to the sensor 331 for station 223. Similarly, timing gate 106B has a first input from clock source 51 through an AND gate 110, a second input from sensor 331, and a third input from excess output 1088 through an inverter 1093. An inverter 100, connected to the output of inverter 109A, applies an inhibit input to AND gate 110. The Product A diversion actuator 744A for station 223 is controlled by the excess signal from output 108A of register 104A, supplied to the actuator through an inverter 112A. The input signal to the Product B diversion actuator 7448 is supplied by an AND gate 306. Gate 306 has one input from an inverter 1128 connected to the excess output 1088 of error register 1048 and a second input from an inverter 305 connected to the output of inverter 112A. The outlet actuator 744C is controlled by the discharge signal for station 223, from sensor 331.

Because the portions of control system 250 associated with any additional secondary discharge stations would be duplicates of those for stations 221-223, no further sections of control system have been illustrated in FIG. 9.

The portion of control system 250 that actuates the master classification station 224 for Product A includes an OR gate 124A having a plurality of inputs, each connected to the deficiency output of the Product A error register for one secondary classification station. Thus, OR gate 124A has input connections from output 67A of error register 64A, from output 87A of error register 84A, from output 107A of error register 104A, etc. For Product B, an AND gate 1248 is provided with an input connection from each of the deficiency outputs 67B, 87B and 1078 of error registers 64B, 84B and 104B, respectively. The output of OR gate 124A is connected, through an inverting amplifier 125A, to one input of the master station Product A timing gate 54A to afford an inhibit signal for that gate. The output of gate 1248 is similarly coupled, through an inverter 125B, to one input of gate 548. The output of inverter 125A is also coupled, through an inverter 120, to another input of timing gate 54B.

The output of OR gate [24A is also connected to an inverting amplifier 122A that is in turn connected to the diversion actuator 444A that controls the diversion of sand from the master classification station 224 to the Product A specification flume 46A (see FIG. 4). Gate 1248 is coupled, through an inverter 122B, to one input of an AND gate 308 that controls the Product B diversion actuator 4445 for the master station 224. Gate 308 has a second input derived from an inverter 307 that is connected to the output of inverter 122A. The outlet actuator 444C for station 224 is connected to the sensor 31 for that station.

The operation of control system 250 is based upon the same fundamental assumption as the previously described systems, that the quantity of sand or other granular material discharged through any one of the outlet valves of tank 210 is approximately proportional to the length of time the valve is held open. The quantities of sand discharged through valve 41, controlled by the outlet actuator 444C and directed to the different flumes by the diversion actuators 444A and 444B, is treated as an independent variable. The quantities of sand discharged to the specification product flumes 46A and 468 from the other tank stations are treated as dependent variables.

When control system 250 (FIG. 9) is first placed in operation, in conjunction with tank 210 (FIG. 4), each of the error registers 64A, 64B, 84A, 848, etc. has a count of zero so that there is no output signal from any error register that would indicate either an excess or a deficiency. Referring first to station 221, with no excess signal output from terminal 68A of error register 64A, inverter 72A supplies an enabling signal to the diversion actuator 544A for Product A at station 221. As a consequence, actuator 544A positions the discharge hose at station 221 over the Product A flume. In a similar manner, the Product A diversion actuators for the other secondary stations, such as actuators 644A and 744A for stations 222 and 223, are energized; each actuator positions the discharge conduit for its station over the Product A flume. Because there is no deficiency signal from any of the error registers, there is no deficiency output signal from OR gate 124A, so that inverter 122A affords an enabling signal to the Product A diversion actuator 444A at the master station 224. Accordingly, the discharge conduit 45 at station 224 (FIG. 4) is positioned over the Product A flume 46A.

When operation is initiated, because there are no deficiency signals from any of the Product B error registers, there is no deficiency output signal from OR gate 1248. As a consequence, inverter 122B supplies an enabling signal to AND gate 308 in the input to the Product B diversion actuator 444B. However, gate 308 is inhibited by the signal from inverter 307, so that actua tor 4448 is not energized at this time. The controls for the secondary stations function in the same manner. Thus, in station 221, because there is no excess signal from output 688 of register 64B, inverter 728 provides an enabling signal to AND gate 302. An inhibiting signal is supplied to gate 302, however, from inverter 30!. Consequently, the Product B diversion actuator 5448 for station 221 is not energized. It is thus seen that, when operation is commenced, all of the discharge hoses at the master and secondary classification stations are positioned over the Product A flume, flume 46A, and all sand discharge is supplied to Product A. At station 221, outlet actuator 544C is energized to open valve 4] whenever an adequate accumulation of sand at the discharge station is indicated by sensor 131 (FIG. 9). The same action occurs with respect to the outlet actuators for the other classification stations of tank 210.

At any given time, while control system 250 is in operation, one of the error registers for Product A may produce an excess signal, indicating that the quantity of sand discharged from its classification station to Prod uct A has become excessive. For example, if more sand has been made available at station 222 than is required for Product A, error register 84A produces an excess signal at terminal 88A. This excess signal, inverted in circuit 92A, de-energizes the Product A diversion actuator 644A, allowing the outlet conduit for station 222 to return to its initial position over the auxiliary discharge flume 46C (FIG. 4). The output from inverter 92A, however, is again inverted in inverter 303 and thus affords an enabling signal input to AND gate 304. Since an enabling signal is already available to gate 304 from inverter 928, as described above, an energizing signal is now supplied to the Product B diversion actuator 6445, which operates to deflect the outlet conduit for station 222 to the Product B flume 468. Thus, whenever the Product A requirements are satisfied at station 222, with respect to Product A, further discharge is diverted to Product B. The same operation takes place at all of the other secondary stations of the tank.

For any given secondary station, such as the stations 221-223, the supply of sand may exceed that required for both Product A and Product B. Under these circumstances, after classification has proceeded for a substantial period of time, there will be an AND signal from both error registers for that particular classification station. Again selecting station 222 as an example, under these circumstances there would be an excess signal at both of the terminals 88A and 88B. The Product A diversion actuator 644A is then cut off by the inverted signal supplied thereto from inverter 92A. The Product B diversion actuator 644B is also out off because, although there is an enabling signal supplied to AND gate 304 from inverter 303, an inhibit signal is now applied to the AND gate from inverter 928. With both of the diversion actuators 644A and 644B thus cut off, the discharge hose for station 222 returns to its initial position over auxiliary flume 46C and any further accumulation of sand at station 222 is discharged to the auxiliary product.

Whenever a deficiency occurs in the quantity of sand available to Product A from any of the secondary stations controlled by system 250 (FIG. 9), there is a deficiency output signal from OR gate 124A. Inversion of this output signal in inverter 122A de-energizes the Product A diversion actuator 444A for master station 224. The same signal is again inverted in inverter 307 and applied as an enabling signal to AND gate 308. Be cause gate 308 is already supplied with an enabling signal from inverter 1228, it energizes the Product B diversion actuator 444B. Accordingly, the discharge hose 45 for station 224 is deflected to a position over the Product 8 flume 468. (FIG. 4). Thus, upon occurrence of a deficiency condition for any of the Product A secondary stations of the classification tank, the master station output is diverted from Product A to Product B.

The output signal from OR gate 124A is also supplied to the master timing gate 54A through inverter 125A.

This is an inhibit signal which, as in the previous embodiments, disables gate 54A and hence interrupts the timing signal input to the Product A ratio controls 61A, 81A, 101A, etc. The output signal from inverter 125A is again inverted in inverter 120 and applied as an enabling signal to the Product 8 master timing gate 548. Accordingly, whenever the master station 224 is conditioned to discharge sand to Product B, a master timing signal is applied to all of the ratio controls for Product B at the various secondary stations, including ratio controls 61B, 8113, 10113, etc.

For some operating conditions, there may be a deficiency of material for a secondary station for Product A, and also a deficiency for a secondary station for Product B. Under these circumstances, the master station Product A diversion actuator 444A is inhibited by the signal from OR gate 124A, through inverter 122A. The master station Product 8 actuator 4448 received an inhibit input from OR gate 1243 through inverter 1228. Thus, when outlet actuator 444C is actuated, the discharge at the master station goes toProduct C, the auxiliary product. At the same time, the ratio controls 61A and 61B are inhibited by the signals supplied from inverters 125A and 1258 to gates 54A and 54B, respectively.

It is thus seen that the ratio controls in system 250 function in the same basic manner as in the previously described systems, except that control system 250 pro vides for sequential preparation of Product A and Product B instead of the simultaneous preparation of the two specification products that is afforded with the control system 150 of FIG. 8. The sequential operation afforded by system 250 is necessary for the mechanical arrangement of the classification stations employed in tank 210 (FIG. 4) because that tank does not include means for simultaneous discharge of sand to the two specification products. A sequential system like system 250 (FIG. 9) can also be applied to tank 10, with its multiple outlets at each classification station, if desired. However, the simultaneous system 150 of FIG. 8 is usually better suited to the multiple-outlet classification station construction.

In system 250, the error registers for the secondary classification stations operate in the same manner as described for previous systems, except that sequential operation is again afforded. Thus, taking station 221 as an example, when an excess signal appears at terminal 68A of error register 64A, diverting subsequent discharge to Product B as described above, the excess signal is inverted in inverter 69A and applied to gate 66A to inhibit that gate and prevent error register 64A from recording an erroneous discharge to Product A. The output signal from inverter 69A is also supplied to inverter 60, which produces an enabling signal that is applied to AND gate 70. Gate 70 remains enabled as long as the discharge to Product B continues, permitting effective operation of error register 648. If the discharge to Product B becomes excessive at Station 221, as indicated by an excess signal at terminal 688, that excess signal is again inverted in inverter 69B and supplied as an inhibiting signal to AND gate 668 so that register 64B does not record an erroneous discharge to Product B when the discharge is actually going to the auxiliary flurne 46C. The same basic operation occurs with respect to the error registers for all of the other secondary classification stations of the tank and hence requires no repetition herein.

Although individual logic circuits are illustrated in the schematic diagrams of the disclosed control systems it will be recognized that this mode of construction is not essential to the present invention. Programmed logic units, of the kinds usually termed "minicomputers" or microprocessors," can be employed to perform part or all of the logic functions of any of control systems 50, 150, or 250 without changing the basic nature or operation of the control system. Moreover, it will be apparent that the precise arrangement of logic disclosed for any of these control systems is subject to change; for example, the sense of the inputs and outputs for the updown counters can be interchanged, and various transformations of the logic (e.g., by deMorgan's theorem) can be effected without change in the basic control operation or end results.

I claim:

1. A control system for a water scalping tank or like apparatus for classifying and reblending granular material in accordance with a quantitative ratio specification, of the kind including a master classification station and a series of secondary classification stations at which different classes of material accumulate at varying rates, each station including a sensor for developing a discharge signal indicative of the presence of sufficient accumulated material to allow discharge at a relatively constant rate for a minimum time interval, each station further including discharge means actuatable between a closed condition in which no material is discharged from the station, a normal discharge condition in which material is discharged to a specification reblending receptacle, and an auxiliary discharge condition in which material is discharged to an auxiliary receptacle, the control system comprising:

a plurality of actuating means, one for each classification station, for actuating the discharge means for that station from its closed condition to a discharge condition in response to a discharge signal from the sensor for that station, and further for actuating the discharge means to its auxiliary discharge condition in response to a diversion signal; plurality of timing means, one for each classification station, for generating a timing signal representative of the time that classification station is in its normal discharge condition;

a series of comparator means, each including a settable ratio control, one comparator for each secondary classification station, for continuously comparing the master station timing signal in pre-set ratio with the secondary station timing signal to develop an excess signal whenever there is an excessive discharge from that secondary station to the specification receptacle and to develop a deficiency signal whenever there is an inadequate discharge from that secondary station to the specification receptacle, the excess signal from each secondary station being applied to the actuating means for that station as a diversion signal;

and means, coupled to all of the comparator means, for applying a diversion signal to the actuating means of the master station upon occurrence of a deficiency signal from any of the comparators.

2. A control system for a classifying and reblending apparatus, according to claim 1, in which each comparator means includes tolerance means for establishing a substantial range of variation from an exact comparison, in which range the comparator means develops neither an excess signal nor a deficiency signal.

3. A control system for a classifying and reblending apparatus, according to claim 1, further comprising a clock source for developing a digital clock signal of constant frequency, in which each timing means comprises AND gate means having at least three input signals applied thereto, those input signals comprising the clock signal and the diversion and discharge signals for the classification station with which the timing means is associated.

4. A control system for a classifying and reblending apparatus, according to claim 3, in which each comparator means comprises an up-down digital counter, having a down input connected to the output of the master station timing means and an up input connected to the output of the timing means of the secondary station with which the comparator means is associated.

5. A control system for a classifying and reblending apparatus, according to claim 4, in which the settable ratio control for each comparator means comprises a settable digital counter interposed between the master station timing means and the up-down counter of that comparator means.

6. A control system for a classifying and reblending apparatus, according to claim 4, in which each comparator means include tolerance means, comprising two AND gates connected to the up-down counter, for inhibiting development of the excess signal and the deficiency signal until a predetermined departure of more than one count from a zero count is recorded in the updown counter.

7. A control system for a classifying and reblending apparatus, according to claim 4, and further comprising reset means for periodically resetting all counters to zero.

8. A control system for a water scalping tank or like apparatus for classifying and reblending granular material into two specification products in accordance with two quantitative ratio specifications of the kind including a master classification station and a series of secondary classification stations at which different classes of material accumulate at varying rates, each station including a sensor for developing a discharge signal indicative of the presence of suffficient accumulated material to allow discharge at a relatively constant rate for a minimum time interval, each station further including discharge means actuatable between a closed condition in which no material is discharged from the station, a first discharge condition in which material is discharged to a first specification reblending receptacle, a second discharge condition in which material is discharged to a second specification reblending receptacle, and an auxiliary discharge condition in which material is discharged to auxiliary receptacle, the control system comprising:

a plurality of actuating means, one for each classification station, for actuating the discharge means for that station from its closed condition to a discharge condition in response to a discharge signal from the sensor for that station, and further for ac tuating the discharge means for that station between its first and second discharge conditions and its auxiliary discharge condition in response to diversion signals;

a first timing means and a second timing means for each classification station, generating a first timing signal representative of the time that classification station is in its first discharge condition and the second timing means generating a second timing signal representative of the time that classification station is in its second discharge condition;

a series of comparator means, each including a settable ratio control, comprising a first comparator and a second comparator for each secondary classification station, the first comparator continuously comparing the master station first timing signal in pre-set ratio with the secondary station first timing signal to develop a first excess signal whenever there is an excessive discharge from that secondary station to the first specification receptacle and to develop a first deficiency signal whenever there is an inadequate discharge from that secondary sta tion to the first specification receptacle, the first excess signal from each secondary station being applied to the actuating means for that station as a first diversion signal to inhibit operation in the first discharge condition,

the second comparator for each secondary classification station continuously comparing the master station second timing signal in pre-set ratio with the secondary station second timing signal to develop a second excess signal whenever there is an excessive discharge from that secondary station to the second specification receptacle and to develop a second deficiency signal whenever there is an inadequate discharge from that secondary station to the second specification receptacle, the second excess signal from each secondary station being applied to the actuating means for that station as a second diversion signal to inhibit operation in the second discharge condition;

first master diversion means, coupled to all of the first comparator means, for applying a first diversion signal to the actuating means of the master station upon occurrence ofa first deficiency signal for any of the secondary stations to inhibit operation in the first discharge condition;

and second master diversion means, coupled to all of the second comparator means, for applying a second diversion signal to the actuating means of the master station upon occurrence of a second deficiency signal for any of the secondary stations.

9. A control system for a classifying and reblending apparatus, according to claim 8, in which the discharge means at each station of the classifying and reblending apparatus includes a separate outlet valve for each receptacle, and in which the actuating means for each station actuates the discharge means to afford simultaneous operation in both the first and second discharge conditions in the absence of any diversion signals for that station.

10. A control system for a classifying and reblending apparatus, according to claim 8, in which, for each station, the actuating means includes a sequential logic circuit that actuates the discharge means to its second discharge condition only when the first diversion signal is present, and that actuates the discharge means to its auxiliary discharge condition only when both the first diversion signal and the second diversion signal are present. 

1. A control system for a water scalping tank or like apparatus for classifying and reblending granular material in accordance with a quantitative ratio specification, of the kind including a master classification station and a series of secondary classification stations at which different classes of mateRial accumulate at varying rates, each station including a sensor for developing a discharge signal indicative of the presence of sufficient accumulated material to allow discharge at a relatively constant rate for a minimum time interval, each station further including discharge means actuatable between a closed condition in which no material is discharged from the station, a normal discharge condition in which material is discharged to a specification reblending receptacle, and an auxiliary discharge condition in which material is discharged to an auxiliary receptacle, the control system comprising: a plurality of actuating means, one for each classification station, for actuating the discharge means for that station from its closed condition to a discharge condition in response to a discharge signal from the sensor for that station, and further for actuating the discharge means to its auxiliary discharge condition in response to a diversion signal; a plurality of timing means, one for each classification station, for generating a timing signal representative of the time that classification station is in its normal discharge condition; a series of comparator means, each including a settable ratio control, one comparator for each secondary classification station, for continuously comparing the master station timing signal in pre-set ratio with the secondary station timing signal to develop an excess signal whenever there is an excessive discharge from that secondary station to the specification receptacle and to develop a deficiency signal whenever there is an inadequate discharge from that secondary station to the specification receptacle, the excess signal from each secondary station being applied to the actuating means for that station as a diversion signal; and means, coupled to all of the comparator means, for applying a diversion signal to the actuating means of the master station upon occurrence of a deficiency signal from any of the comparators.
 2. A control system for a classifying and reblending apparatus, according to claim 1, in which each comparator means includes tolerance means for establishing a substantial range of variation from an exact comparison, in which range the comparator means develops neither an excess signal nor a deficiency signal.
 3. A control system for a classifying and reblending apparatus, according to claim 1, further comprising a clock source for developing a digital clock signal of constant frequency, in which each timing means comprises AND gate means having at least three input signals applied thereto, those input signals comprising the clock signal and the diversion and discharge signals for the classification station with which the timing means is associated.
 4. A control system for a classifying and reblending apparatus, according to claim 3, in which each comparator means comprises an up-down digital counter, having a down input connected to the output of the master station timing means and an up input connected to the output of the timing means of the secondary station with which the comparator means is associated.
 5. A control system for a classifying and reblending apparatus, according to claim 4, in which the settable ratio control for each comparator means comprises a settable digital counter interposed between the master station timing means and the up-down counter of that comparator means.
 6. A control system for a classifying and reblending apparatus, according to claim 4, in which each comparator means include tolerance means, comprising two AND gates connected to the up-down counter, for inhibiting development of the excess signal and the deficiency signal until a predetermined departure of more than one count from a zero count is recorded in the up-down counter.
 7. A control system for a classifying and reblending apparatus, according to claim 4, and further comprising reset means for periodically resetting all counters to zero.
 8. A control system for a water scalping Tank or like apparatus for classifying and reblending granular material into two specification products in accordance with two quantitative ratio specifications of the kind including a master classification station and a series of secondary classification stations at which different classes of material accumulate at varying rates, each station including a sensor for developing a discharge signal indicative of the presence of suffficient accumulated material to allow discharge at a relatively constant rate for a minimum time interval, each station further including discharge means actuatable between a closed condition in which no material is discharged from the station, a first discharge condition in which material is discharged to a first specification reblending receptacle, a second discharge condition in which material is discharged to a second specification reblending receptacle, and an auxiliary discharge condition in which material is discharged to auxiliary receptacle, the control system comprising: a plurality of actuating means, one for each classification station, for actuating the discharge means for that station from its closed condition to a discharge condition in response to a discharge signal from the sensor for that station, and further for actuating the discharge means for that station between its first and second discharge conditions and its auxiliary discharge condition in response to diversion signals; a first timing means and a second timing means for each classification station, generating a first timing signal representative of the time that classification station is in its first discharge condition and the second timing means generating a second timing signal representative of the time that classification station is in its second discharge condition; a series of comparator means, each including a settable ratio control, comprising a first comparator and a second comparator for each secondary classification station, the first comparator continuously comparing the master station first timing signal in pre-set ratio with the secondary station first timing signal to develop a first excess signal whenever there is an excessive discharge from that secondary station to the first specification receptacle and to develop a first deficiency signal whenever there is an inadequate discharge from that secondary station to the first specification receptacle, the first excess signal from each secondary station being applied to the actuating means for that station as a first diversion signal to inhibit operation in the first discharge condition, the second comparator for each secondary classification station continuously comparing the master station second timing signal in pre-set ratio with the secondary station second timing signal to develop a second excess signal whenever there is an excessive discharge from that secondary station to the second specification receptacle and to develop a second deficiency signal whenever there is an inadequate discharge from that secondary station to the second specification receptacle, the second excess signal from each secondary station being applied to the actuating means for that station as a second diversion signal to inhibit operation in the second discharge condition; first master diversion means, coupled to all of the first comparator means, for applying a first diversion signal to the actuating means of the master station upon occurrence of a first deficiency signal for any of the secondary stations to inhibit operation in the first discharge condition; and second master diversion means, coupled to all of the second comparator means, for applying a second diversion signal to the actuating means of the master station upon occurrence of a second deficiency signal for any of the secondary stations.
 9. A control system for a classifying and reblending apparatus, according to claim 8, in which the discharge means at each station of the classifying and reblending apparatus includes a separate outlet valve for each receptacle, and in which the actuating means for each station actuates the discharge means to afford simultaneous operation in both the first and second discharge conditions in the absence of any diversion signals for that station.
 10. A control system for a classifying and reblending apparatus, according to claim 8, in which, for each station, the actuating means includes a sequential logic circuit that actuates the discharge means to its second discharge condition only when the first diversion signal is present, and that actuates the discharge means to its auxiliary discharge condition only when both the first diversion signal and the second diversion signal are present. 